"Bill Daniels" wrote in message
...

"Mike Rapoport" wrote in message
ink.net...
Water injection does not increase efficiency, it lowers it. The water
goes
in as a liquid and goes out as a gas. The energy to do that comes from
burning fuel. It will always take more fuel to produce a given amount of
power with water injection than without. Water injection does allow
higher
MP or higher compression so the engine can produce more power. Piston
engine fighters used it for more peak horsepower and some turbines use it
for the same purpose but it definately come at the price of higher fuel
burn
per horsepower.

Mike

Hmm, consulting my ancient copy of Ricardo's "High Speed Internal
Combustion
Engines", Sir Harry said that water injection can be substituted for any
excess fuel consumed for the purpose of reducing cylinder temperature
and/or
increasing detonation margin. Further, evaporation of the water reduces
the
intake charge temperature so as to reduce pumping losses. He goes on to
say
that, while there is energy lost to evaporating the water droplets, the
overall fuel economy of an aircraft engine at max power setting will be
improved by use of water injection particularly if the compression ratio
has
been increased to take advantage of the increased detonation margin.

Bill Daniels


Yes, water injection can replace fuel used for cooling. I was not precise
enough in my wording. In the case of using water injection at lower power
settings (where excess fuel for cooling is not used) efficiency will be
reduced. I used water injection in a Corvette that had 11:1 compression to
stop detonation. It worked but power was definately less than with high
octane gasoline and without water injection.

Mike